Transmission lines are the basic building blocks of any RF and microwave circuits. The width of a microstripline increases as the characteristic impedance is lowered for a given substrate. Wide microstriplines suffer from spurious and higher order modes at higher frequencies and may not behave as transmission lines. This means the lower limitation for a realisable microstripline is about 10 ohm. In this project microstriplines with characteristic impedances of 7 ohm and 25 ohm at a frequency of 2 GHz were designed and realised using the artificial transmission lines (ATL) concept. Detailed theoretical analysis and circuit and EM simulations were used for the design and implementation of the ATLs. Taconic TLY-5 substrate was used for the PCB fabrication. The substrate thickness was 0.787 mm and the dielectric constant was 2.2. The measured results were de-embedded and compared with the simulation results. The detailed procedure of modelling and de-embedding of an SMA connector is also given. The 25 ohm ATL was realised using microstriplines only, where as microstriplines and chip capacitors were used in realising the 7 ohm ATL. The measured characteristic impedance of the 25 ohm ATL was 24.4 ohm and the measured electrical length of the 25 ohm ATL was 180 degrees at 2.1 GHz. To realise a 25 ohm ATL with 90 degrees electrical length, the half-wavelength 25 ohm ATL geometry was cut into half and one of the half geometries was EM simulated. The EM simulated electrical length of the 25 ohm ATL was 90 degrees at 1.9 GHz. The measured characteristic impedance of the 7 ohm ATL was 5.9 ohm and the measured electrical length of the 7 ohm ATL was 90 degrees at 1.8 GHz. The main advantage of an ATL is size reduction. A 25 ohm meandered microstrip line (substrate thickness = 0.787 mm, dielectric constant = 2.2) with 180 degrees electrical length at 2 GHz has a size of 34 mm x 15 mm. The 25 ohm ATL with 180 degrees electrical length at 2.1 GHz was realised in a size of 22 mm x 19 mm. The design of the 25 Ω ATL resulted in 18 percent reduction in area compared to the meander line. A 7 ohm conventional microstripline (substrate thickness = 0.787 mm, dielectric constant = 2.2) with 90 degrees electrical length at 1.8 GHz has a size of about 28 mm x 27 mm. The 7 ohm ATL with 90 degrees electrical length at 1.8 GHz was realised in a size of 7 mm x 8.4 mm which is only 8 percent of the conventional 7 ohm microstripline area. In general, a spacing of 3h where h is the substrate thickness is required between the adjacent microstriplines. In this project detailed investigations were done to see if the spacing can be reduced without any detrimental coupling affects and a spacing of 0.6 mm was used. This reduction in spacing has resulted in reduced size of the ATL. For an asymmetrical power splitter based on the Wilkinson topology, the power splitter output power split ratio depends on the square of the characteristic impedances of the quarter-wavelength arms. In this project an asymmetrical power splitter was designed and realised using a 7 ohm ATL and a 25 ohm ATL as the quarter-wavelength arms. The desired centre frequency of the power splitter was 2 GHz and the measured centre frequency was 1.6 GHz. At the centre frequency the phase difference between the output ports of the power splitter will be zero. The simulated power split ratio was 10.1 dB and the measured power split ratio was 13 dB. The power split ratio calculated using the measured characteristic impedances of the ATLs (24.4 ohm and 5.9 ohm) will be 12.4 dB which is very close to the measured power split ratio.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-03-08T12:15:41Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DissertaçãoDaviLira.pdf: 3636018 bytes, checksum: a3d66cf7d5a7e3e102b2d49abcabf422 (MD5) / Made available in DSpace on 2017-03-08T12:15:41Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DissertaçãoDaviLira.pdf: 3636018 bytes, checksum: a3d66cf7d5a7e3e102b2d49abcabf422 (MD5) Previous issue date: 2016-04-13 / O presente trabalho introduz um novo método para confecção de acopladores híbridos do tipo branch-line que sejam de banda dupla, ou seja, que são projetados para operar em duas frequências desejadas quaisquer com a mesma resposta. Este método faz uso de uma nova estrutura de linha de transmissão artificial (LTA) implementada em microfita, a qual é composta por três linhas de transmissões conectadas em cascata, com estubes em aberto inseridos em paralelo entre as linhas de transmissão. Foram obtidas expressões algébricas que determinam, em função das frequências das bandas desejadas, os valores de impedância característica e comprimento elétrico de cada um dos segmentos e estubes para que, em ambas as frequências, a LTA tenha os mesmos parâmetros de espalhamento que, e portanto seja equivalente a, um único segmento de linha de transmissão convencional com impedância característica e comprimento elétrico quaisquer especificados. Para obter o acoplador híbrido do tipo branch-line com banda dupla, portanto, substituímos cada linha de transmissão do acoplador por uma ATL com os parâmetros calculados de acordo com as expressões encontradas. Essa técnica foi usada para projetar, simular, fabricar e medir um acoplador híbrido branch-line que funcionasse nas frequências GSM de 925MHz e ISM 5.8GHz. Essa técnica tem como principal vantagem a capacidade e a flexibilidade de obter acopladores branch-line com bom desempenho em duas bandas quaisquer. / This work deals with a new method for the design of dual band branch-line hybrid couplers with arbitrary central frequencies, in other words, branch-line couplers which operate in two desired frequencies. This method makes use of a new artificial transmission line (ATL) structure, which is composed of the cascade connection of three transmission lines segments with parallel open stubs between them. Algebraic expressions were obtained that specify, in function of the central frequencies, the values for the characteristic impedance and electric length of the segments, so that the ATL has, for both frequencies, the same scattering parameters, hence the same behavior, as an ordinary transmission line with any chosen characteristic impedance and electric length. To obtain a dual band branch line coupler, the desired frequencies are chosen and the expressions are evaluated to find out the characteristic impedances and electric lengths of the ATL’s to replace all transmission lines that make up the coupler. This technique was used to design, simulate, fabricate and measure a branch-line hybrid coupler that works on the 925MHz GSM and 5.8GHz ISM frequencies. This technique has as it’s main advantage the ability and flexibility to yield couplers with good performance in two arbitrary bands.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-07-20T14:10:52Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação_Leonardo_digital.pdf: 8248572 bytes, checksum: 8eaff05e901397f38f65a651841ef367 (MD5) / Made available in DSpace on 2017-07-20T14:10:52Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação_Leonardo_digital.pdf: 8248572 bytes, checksum: 8eaff05e901397f38f65a651841ef367 (MD5) Previous issue date: 2015-01-22 / CAPES / O presente trabalho aborda o desenvolvimento e a implementação de acopladores híbridos em quadratura mais compactos e com largura de banda e desempenho similares as do acoplador branch-line convencional. Para isso, fez-se uso de uma classe de estruturas denominadas linhas de transmissão artificiais (LTA). Uma nova estrutura desse tipo, composta por três linhas de transmissão conectadas em cascata, é analisada e utilizada neste trabalho. Foram derivadas equações matemáticas para o projeto deste tipo de estrutura que podem ser utilizadas para obter LTAs com uma matriz de espalhamento idêntica, para uma dada frequência de operação, a de uma linha de transmissão com uma impedância característica e comprimento elétrico quaisquer. Essa técnica foi aplicada no projeto de acopladores híbridos em quadratura em microfita para as bandas GSM em 920 MHz e ISM em 2.45 GHz usando-se o substrato FR-4 com espessura de 1.6 mm. Obteve-se dispositivos com áreas aproximadamente 70% menor do que a área do acoplador branch-line convencional operando em 920 MHz e aproximadamente 50% menor do que o acoplador de 2.45 GHz. Os acopladores obtidos foram simulados, fabricados e medidos, mostrando que os seus desempenhos são comparáveis aos dos acopladores convencionais. A técnica desenvolvida neste trabalho é geral o suficiente para ser aplicada ao projeto de outros dispositivos que usem trechos de linhas de transmissão. / This thesis is concerned with the design and implementation of compact hybrid couplers with similar bandwidth and performance to the conventional branch-line coupler. To achieve this, a class of structures, called artificial transmission line (ATL), was used. A new structure of this type, made of three transmission lines connected in cascade, is analyzed and used. Mathematical equations have been derived for the design of this type of structure that can be used to obtain ATLs with an identical scattering matrix, for a given frequency of operation, to that of a transmission line with a given characteristic impedance and electrical length. This technique was applied in the design of microstrip quadrature hybrid couplers for the 920 MHz GSM band and for the 2.45 GHz ISM band using a 1.6 mm-thick FR-4 substrate. These couplers have surface areas approximately 70% smaller than the area of the conventional branch-line coupler operating at 920 MHz and approximately 50% for the 2.45 GHz coupler. The couplers obtained were simulated, manufactured and tested, showing that their performances are comparable to the conventional coupler. The technique developed here is general enough to be applied to the design of other devices using transmission line sections.

RF and microwave applications represent one of the fastest-growing segments of the high performance electronics market, where ongoing innovation is critical. Manufacturers compete intensively to meet market needs with reduced cost, size, weight and many other performance criteria demands. Under this scenario, transmission lines based on metamaterial concepts can be considered a very interesting alternative to the conventional transmission lines. They are more compact (compatible with planar manufacturing processes) and present higher degrees of design flexibility. Furthermore, metamaterial transmission lines can also provide many other unique properties not achievable with ordinary transmission lines, such as dispersion or impedance engineering. Nevertheless, the impact in the industry is still not relevant, mostly due to the complexity of the related synthesis and design procedures. These procedures are mainly based on the engineer’s experience, with the help of costly full-wave electromagnetic (EM) simulators and parameter extraction methods. The aim of this thesis is to contribute to simplify and speed up the synthesis and design procedures of artificial transmission lines. In particular, the lines obtained by periodically loading a conventional transmission line with electrically small resonators, such as split ring resonators (SSRs) or its complementary particle (CSRR). The design procedure is automated by using Space Mapping techniques. In contrast to other alternative methods, real synthesis is found from the circuit schematic (that provides a given target response) and without need of human intervention. Some efforts to make the method practical and useful have been carried out. Given a certain target response, it is determined whether it can be physically implemented with a chosen technology, and hence proceeding next to find the synthesis, or not. For this purpose, a two-step Aggressive Space Mapping approach is successfully proposed. In contrast to other methods, the real synthesis is found from certain target circuit values (corresponding to the equivalent circuit model that characterizes the structure to be synthesized). Different efforts have been carried out in order to implement a useful and practical method. Some of them were focused to determine if, given certain circuit parameters (which determine the target response) and certain given technology specifications (permittivity and height of the substrate, technology limits), that response is physically realizable (convergence region). This technique was successfully formulated and it is known as “Two-Step Aggressive Space Mapping Approach”. In this work, the latest improvements made till date, from the synthesis of basic unit cells until different applications and kinds of metamaterial-based circuits, are presented. The results are promising and prove the validity of the method, as well as its potential application to other basic cells and more complex designs. The general knowledge gained from these cases of study can be considered a good base for a coming implementation in commercial software tools, which can help to improve its competitiveness in markets, and also contribute to a more general use of this technology. / Rodríguez Pérez, AM. (2014). Synthesis of Planar Microwave Circuits based on Metamaterial Concepts through Aggressive Space Mapping [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48465 / TESIS